ALSA: usb-audio: prevent CH345 multiport output SysEx corruption

The CH345 USB MIDI chip has two output ports.  However, they are
multiplexed through one pin, and the number of ports cannot be reduced
even for hardware that implements only one connector, so for those
devices, data sent to either port ends up on the same hardware output.
This becomes a problem when both ports are used at the same time, as
longer MIDI commands (such as SysEx messages) are likely to be
interrupted by messages from the other port, and thus to get lost.

It would not be possible for the driver to detect how many ports the
device actually has, except that in practice, _all_ devices built with
the CH345 have only one port.  So we can just ignore the device's
descriptors, and hardcode one output port.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Cc: stable@vger.kernel.org
Signed-off-by: Takashi Iwai <tiwai@suse.de>

4 files changed, 16 insertions, 0 deletions

diff --git a/sound/usb/midi.c b/sound/usb/midi.c
index 68e9f9a83fde..010094abf752 100644
--- a/sound/usb/midi.c
+++ b/sound/usb/midi.c
@@ -2379,6 +2379,9 @@ int snd_usbmidi_create(struct snd_card *card,
 
                 err = snd_usbmidi_detect_per_port_endpoints(umidi, endpoints);
                 break;
+        case QUIRK_MIDI_CH345:
+                err = snd_usbmidi_detect_per_port_endpoints(umidi, endpoints);
+                break;
         default:
                 dev_err(&umidi->dev->dev, "invalid quirk type %d\n",
                         quirk->type);
diff --git a/sound/usb/quirks-table.h b/sound/usb/quirks-table.h
index 1a1e2e4df35e..c60a776e815d 100644
--- a/sound/usb/quirks-table.h
+++ b/sound/usb/quirks-table.h
@@ -2829,6 +2829,17 @@ YAMAHA_DEVICE(0x7010, "UB99"),
         .idProduct = 0x1020,
 },
 
+/* QinHeng devices */
+{
+        USB_DEVICE(0x1a86, 0x752d),
+        .driver_info = (unsigned long) &(const struct snd_usb_audio_quirk) {
+                .vendor_name = "QinHeng",
+                .product_name = "CH345",
+                .ifnum = 1,
+                .type = QUIRK_MIDI_CH345
+        }
+},
+
 /* KeithMcMillen Stringport */
 {
         USB_DEVICE(0x1f38, 0x0001),
diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
index 5ca80e7d30cd..7016ad898187 100644
--- a/sound/usb/quirks.c
+++ b/sound/usb/quirks.c
@@ -538,6 +538,7 @@ int snd_usb_create_quirk(struct snd_usb_audio *chip,
                 [QUIRK_MIDI_CME] = create_any_midi_quirk,
                 [QUIRK_MIDI_AKAI] = create_any_midi_quirk,
                 [QUIRK_MIDI_FTDI] = create_any_midi_quirk,
+                [QUIRK_MIDI_CH345] = create_any_midi_quirk,
                 [QUIRK_AUDIO_STANDARD_INTERFACE] = create_standard_audio_quirk,
                 [QUIRK_AUDIO_FIXED_ENDPOINT] = create_fixed_stream_quirk,
                 [QUIRK_AUDIO_EDIROL_UAXX] = create_uaxx_quirk,
diff --git a/sound/usb/usbaudio.h b/sound/usb/usbaudio.h
index 15a12715bd05..b665d85555cb 100644
--- a/sound/usb/usbaudio.h
+++ b/sound/usb/usbaudio.h
@@ -95,6 +95,7 @@ enum quirk_type {
         QUIRK_MIDI_AKAI,
         QUIRK_MIDI_US122L,
         QUIRK_MIDI_FTDI,
+        QUIRK_MIDI_CH345,
         QUIRK_AUDIO_STANDARD_INTERFACE,
         QUIRK_AUDIO_FIXED_ENDPOINT,
         QUIRK_AUDIO_EDIROL_UAXX,